Famicom with Audio Buzzing

[dc16]

This is the third Famicom I AV modded, and I'm having one particular problem with this one. Whenever a game plays on it, a faint buzzing sound is heard. There is no buzzing when I activate it on a blank screen. There is no buzzing from the video side. For this one, I followed that usual guide, a 220uF cap from line 46.

Among things, getting games to run, even after they are cleaned minimally is a pain, plus the pins look rather dry. The .01uF ceramic capacitors on the transistor side of the board seem to be kind of faded, or blown out, if that's a thing.

I'm just wondering what are the common causes for audio buzzing if the circuit is way less complicated than the one for composite.

If it's just the cartridge connector, I should use some Deoxit on it, and it should clear up the problem right? I will continue investigating in a few days from now.

[chowder]

Microphone buzz from the second controller?  Try disconnecting it and see if the problem goes away.

@80sFREAK why should how many AV-modded Famicoms he has concern you?  He says third one that he has modded, so maybe he's doing them for other people.

[zmaster18]

There's nothing wrong with doing a bunch of Famicoms Another source of buzzing is if you aren't using the original AC adapter with proper voltage output.

[dc16]

This is my third one because they're so cheap and small compared to an NES. It's pretty hard to get an NES for cheap in my area because of resellers.

It's not my power supply, because I have two others and I'm not getting this problem when I use the same AC adapter. Radial caps and 7805 have been replaced. Nor is it the controllers, because I unplug them when doing this mod.

Could it also be a bad ground? I did attach the ground lead for the RCA jacks to a point somewhere to the close of the unit. The ground for the transistor is also the same point as it was originally, under the tape.


Will continue to investigate, thanks for your suggestions.

[80sFREAK]

Clean up slider in the second controller.
/thread

chowder, If you doing modding for other people and don't know, how to do, it's a shame.

[chowder]

Clean up slider in the second controller.
/thread

chowder, If you doing modding for other people and don't know, how to do, it's a shame.

He already said he unplugged the controllers.  As to the second part, I have no idea what you're talking about 

[80sFREAK]

Is it buzzing or some sort of distortion?

[dc16]

When the game loads, a steady buzzing is heard. It can be drowned out by music though.

[hvc01]

Less is best...remove those capacitors for a start. The one on the left is touching apears to be touching another pin it shouldn't be.

[dc16]

It's not. That ceramic capacitor is soldered to pins 20 and 22, as the guide says. And would that affect the audio?

[hvc01]

I'm not sure but I would do the basic mod first without the capacitors which aren't needed to get clear audio. Maybe see if you can get audio from pin 46 and ground below it first.

[80sFREAK]

It might be '368 chip, one of the gates working as amplifier. U7 to be exact.
Here is hotglue boy started thread with good pic of audio circuit
http://16bitgamer.canadian-forum.com/t356-new-av-famicom-audio-mod-nesamp

[dc16]

It's definitely the audio circuit that leads to pin 46. I replaced a few more capacitors, and I still get the buzzing. At least it's manageable.

[80sFREAK]

Just thought about audio circuit. If you have a look at LM386(or any other IC amplifier) datasheet, you will find, that output grounded via RC(0.1uF and 2.2-4.7R in serial), not just C8 0.1uF. This might be reason for failing U7 over the time.

[dc16]

Thanks. I tested the unit on a different tv, this time a Trinitron. I don't hear the audio buzzing anymore. But the weird thing about this unit is that I see two dark rectangles moving down the background as noise, when the unit is on a all color screen.. No jailbars on this one, as this particular unit had pin 21 separated from the board. My other units have very faint jailbars as usual, but none of that dark rectangle stuff.